1. Field of the Invention
The present invention relates to a control apparatus for and a control method of a variable valve timing mechanism which changes a rotational phase of a camshaft relative to a crankshaft, to vary valve timing of an intake valve and/or an exhaust valve.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 2004-019658 discloses one typical example of a variable valve timing mechanism which utilizes a reaction force transmitted from an engine valve to a cam, to cause transfer of oil between an advance chamber and a retard chamber, thereby varying a rotational phase of a camshaft relative to a crankshaft.
Here, a direction on which cam torque acts is periodically reversed in synchronism with the engine rotation, and an oil transfer direction is determined depending on the direction on which the cam torque acts.
Accordingly, for example, even if a passageway for transferring the oil from the advance chamber toward the retard chamber is opened, the transfer of oil occurs from the advance chamber to the retard chamber only when the cam torque corresponding to the transfer direction is generated.
Therefore, if computation of a manipulated variable for a feedback control is carried out by a control means at every constant time, the computation of the manipulated variable might be repeated in a state where no transfer of oil occurs for the reason that the direction on which the cam torque acts does not correspond to a direction to which the oil is to be transferred. Further, if the computation of the manipulated variable is repeated without occurrence of transfer of the oil, the manipulated variable might be excessively changed since a deviation in the feedback controlling is not reduced, resulting in an occurrence of the overshooting or the hunting.